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L T Furcht

Publications and source records attributed to L T Furcht.

153 records · Page 9Linked to original sources
PubMed1975

Modulation of the distribution of plasma membrane intramembranous particles in contact-inhibited and transformed cells.

The intrinsic organization of the plasma membrane differs in normal and transformed cells. With the technique of freeze fracture and electron microscopy contact inhibited 3T3 cells have been shown to contain aggregated plasma membrane intramembranous particles, while transformed cells demonstrate a uniform particle distribution. The distribution of intramembrous particles in transformed cells can be affected by colchicine or vinblastine which induces a dose- and time-dependent particle aggregation. These observations suggest that microtubules and other membrane-associated colchicine-sensitive proteins probably influence the distribution of intrinsic membrane proteins and intramembranous particles in nucleated mammalian cells. An aggregated particle distribution has been observed in 3T3 cells or colchicine-treated transformed cells frozen in media, phosphate-buffered saline or following brief exposure to glycerol, sucrose or dimethyl sulfoxide containing solutions, independent of whether specimens were rapidly frozen from 37 degrees C, room temperature or 4 degrees C incubations. Cells briefly stabilized in 1% formaldehyde yields similar patterns of particle distribution as cells rapidly frozen in media or cryoprotectants. Glutaraldehyde fixation of cells, however, appears to alter the fracturing process in these cells, as visualized by an altered fracture face appearance, decreased numbers of particles, and no particle aggregates. Differences in membrane organization between normal and transformed cells have therefore been demonstrated using a series of preparative methods and colchicine and vinblastine have been shown to modulate intramembranous particle distribution in transformed 3T3 cells.

Cell Aggregation↗
PubMed1974

Differences in membrane fluidity and structure in contact-inhibited and transformed cells.

Studies on contact-inhibited mouse embryo fibroblast 3T3 cells and 3T3 cells transformed by oncogenic RNA and DNA viruses and by a chemical carcinogen have demonstrated differences in plasma membrane architecture. Spin-label and freeze-fracture ultrastructural studies have shown that contact-inhibited cells have ordered membrane lipids and aggregated intramembranous particles, whereas transformed cells have fluid membrane lipids and randomly distributed intramembranous particles. These findings suggest a model for how changes in the cell membrane may account for some of the characteristic differences observed between contact-inhibited and transformed cells.

Animals↗
PubMed1973

Changes in membrane structure associated with cell contact.

Ultrastructural analysis of 3T3 fibroblasts by freeze-cleavage has demonstrated significant changes in cell-membrane structure associated with cell-to-cell contact and malignant transformation. These changes consist of a rearrangement and redistribution of intramembranous particles on the membrane fracture faces exposed by freeze-cleavage. The results show that noncontacted 3T3 cells in low density contain randomly distributed intramembranous particles. With the development of cell-to-cell contacts during the logarithmic phase of growth however, a pronounced aggregation of intramembranous particles is seen. A direct correlation between the degree of cell contact and the percentage of cells showing intramembranous-particle aggregation has been established. By contrast, transformed SV3T3 and SP3T3 cells show no evidence of intramembranous-particle aggregation even at cell densities where cell-to-cell contact is extensive. In view of recent reports that intramembranous particles represent foci of interaction between certain intrinsic membrane proteins and lipids, we propose that cell-to-cell contact of nontransformed 3T3 cells may initiate a change in the distribution of intrinsic membrane proteins associated with intramembranous particles and that these changes may influence control of cell proliferation.

Animals↗
PubMedDate not supplied

Growth cone migration across extracellular matrix components depends on integrin, but migration across glioma cells does not.

To promote neurite elongation, nerve growth cones must adhere to other surfaces. A complex of integral membrane glycoproteins mediates cell binding to the extracellular glycoproteins fibronectin and laminin (Horwitz et al., J Cell Biol 101:2134-2144, 1985). The receptor complex, named integrin, binds to fibronectin by recognition of a specific peptide sequence, Arg-Gly-Asp-Ser (RGDS), in the fibronectin molecule (Pierschbacher and Ruoslahti, Proc Natl Acad Sci USA 81:5985-5988, 1984). We have used antibodies to integrin and an RGDS synthetic peptide to probe the functions of integrin in the migration of growth cones extended from sensory and spinal cord neurons of chick embryos. Analyses of time lapse videotapes of growth cone migration before and after adding RGDS indicated that 2 mM RGDS rapidly inhibits growth cone movement on substrata coated with fibronectin or a fragment of fibronectin containing the RGDS sequence. RGDS has no effect on growth cone movement on laminin or on a surface coated with material deposited from heart conditioned medium. However, a monclonal antibody to the integrin complex (10 micrograms/ml CSAT) completely blocks growth cone movement on substrata treated with fibronectin, laminin, or heart conditioned medium. Thus integrin may be involved in growth cone adhesion to several extracellular molecules, although the selective effects of RGDS indicate that the integrin complex may have heterogeneous sites for interaction with different components of the extracellular matrix. CSAT antibody has no discernible effect, however, on growth cone migration across the upper surfaces of C6 glioma cells. These data indicate that the surfaces of nerve growth cones contain multiple binding molecules that mediate different adhesive interactions during migration.

Animals↗
PubMedDate not supplied

Cell adhesion and neurite extension in response to two proteolytic fragments of laminin.

Studies from several laboratories have suggested that laminin contains at least two domains that selectively mediate cell type-specific behavior. In this study, two proteolytic fragments of laminin are evaluated for their ability to interact with three different populations of embryonic chicken cells. A 600 kDa thrombin fragment, derived from the central portion of the laminin molecule, supports attachment of dorsal root ganglion (DRG), spinal cord (SC), and heart cells. Neurons from both DRGs and SCs extend neurites in response to this fragment. Quantitatively, both cell adhesion and neurite extension on the 600 kDa fragment are comparable to these responses to intact laminin. A 440 kDa chymotrypsin fragment, derived from either intact laminin or the 600 kDa fragment, does not support equivalent responses. Fewer DRG cells attach to this fragment and neurites are shorter than on the 600 kDa fragment. Heart and SC cell attachment is also reduced in comparison with activity of the 600 kDa fragment, and SC neurites do not form on the 440 kDa fragment. These results suggest that there are at least two cell binding domains in the laminin molecule, one with which a variety of cell types can interact and another that may mediate more restricted cellular responses. The latter site appears to be relatively inactive for SC and heart cell adhesion but supports limited attachment and neurite extension by DRG neurons.

Animals↗